A Computational Investigation of the Multi-Hit Ballistic-Protection Performance of Laminated Transparent-armor Systems

Multi-hit ballistic-protection performance of a prototypical laminated glass/polycarbonate transparent armor is investigated using a series of transient nonlinear dynamics analyses of armor impact with a sequence of four M2AP full metal jacket (FMJ) armor-piercing bullets. All calculations were carried out using ABAQUS/Explicit commercial finite element program (ABAQUS Version 6.7, User Documentation, Dessault Systems, 2007), and the computational results obtained were compared to their experimental counterparts obtained by Dolan (Ballistic Transparent-armor Testing Using a Multi-hit Rifle Pattern, Bachelors, Thesis, Kettering University, December 2007). The comparison revealed that (a) The proposed computational procedure can reasonably well account for the observed multi-hit ballistic-protection performance of the laminated transparent armor; (b) The role of prior bullet hits in reducing armor??s ballistic-protection performance is clearly revealed; (c) The role of polycarbonate lamina in preventing glass fragments from entering the vehicle interior is clearly demonstrated; and (d) Experimentally observed inability of the transparent armor to defeat 0.50-caliber Fragment Simulating Projectiles (FSPs) is confirmed.     

A crystal plasticity materials constitutive model for polysynthetically-twinned γ-TiAl + α2-Ti3Al single crystals

Deformation behavior of polysynthetically-twinned lamellar -TiAl + ₂-Ti₃Al single crystals has been analyzed using a three-dimensional, isothermal, rate-dependent, large-strain, crystal-plasticity based materials constitutive model. Within the model it is assumed that plastic deformation parallel to the -TiAl/₂-Ti₃Al lamellar boundaries is controlled by the softer -TiAl phase while deformation which contains a component normal to these boundaries is dominated by the harder ₂-Ti₃Al phase. The parameters appearing in the crystal-plasticity materials constitutive relations are assessed using the available experimental information pertaining to the active slip systems, their deformation resistances and hardening and rate behavior of the two constitutive phases both in their single-crystalline and in polysynthetically-twinned lamellar forms. The constitutive relations are implemented in a Vectorized User Material Subroutine (VUMAT) of the commercial finite element program Abaqus/Explicit within which the material state is integrated during loading using an explicit Euler-forward formulation. The results obtained suggest that the adopted crystal-plasticity model and the parameters assessed in the present work account quite well for the observed room-temperature deformation behavior of polysynthetically-twinned lamellar -TiAl + ₂-Ti₃Al single crystals.     

Lattice Boltzmann method based computation of the permeability of the orthogonal plain-weave fabric preforms

Changes in the permeability tensor of fabric preforms caused by various modes of fabric distortion and fabric-layers shifting and compacting is one of the key factors controlling resin flow during the infiltration stage of the common polymer-matrix composite liquid-molding processes. While direct measurements of the fabric permeability tensor generally yield the most reliable results, a large number of fabric architectures used and numerous deformation and layers rearrangement modes necessitates the development and the use of computational models for prediction of the preform permeability tensor. The Lattice Boltzmann method is used in the present work to study the effect of the mold walls, the compaction pressure, the fabric-tows shearing and the fabric-layers shifting on the permeability tensor of preforms based on orthogonal balanced plain-weave fabrics. The model predictions are compared with their respective experimental counterparts available in the literature and a reasonably good agreement is found between the corresponding sets of results.     

Crystal plasticity-based finite element analysis of deformation and fracture of polycrystalline lamellar γ-Tial + α2-Ti3al alloys

Deformation behavior of fully-lamellar polycrystalline -TiAl + ₂-Ti₃Al alloys has been analyzed using a finite element method. A three-dimensional rate-dependent, finite-strain, crystal-plasticity based materials constitutive model is used to represent the deformation behavior of the bulk material. The constitutive behavior of -TiAl/-TiAl lamellar interfaces and lamellae-colony boundaries, on the other hand, are modeled using a cohesive-zone formulation. The interface/boundary potentials used in this formulation are determined through the use of atomistic simulations of the interface/boundary decohesion. The constitutive relations for both the -TiAl + ₂-Ti₃Al bulk material and the lamellar interfaces and colony boundaries are implemented in the commercial finite element program Abaqus/Standard within which the material state is integrated using an Euler-backward implicit formulation. The results obtained show that plastic flow localizes into deformation bands even at an overall strain level of only 0.5% and that incompatibilities in plastic flow between the adjacent colonies can give rise to high levels of the hydrostatic stress and, in turn, to intercolony fracture. Furthermore, it is found that when lamellar interfaces are admitted into colonies, fracture is delayed and the materials fail in a more gradual manner.     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.     

Micro-mechanics based derivation of the materials constitutive relations for carbon-nanotube reinforced poly-vinyl-ester-epoxy based composites

The atomic-level computational results of the mechanical properties of Multi-Walled Carbon Nanotube (MWCNT) reinforced poly-vinyl-ester-epoxy obtained in our recent work [Grujicic M, Sun Y-P, Koudela KL (2006) Appl Surf Sci (accepted for publication, March)], have been utilized in the present work within a continuum-based micro-mechanics formulation to determine the effective macroscopic mechanical properties of these materials. Since the MWCNT reinforcements and the polymer-matrix molecules are of comparable length scales, the reinforcement/matrix interactions which control the matrix-to-reinforcement load transfer in these materials are accounted for through direct atomic-level modeling of the “effective reinforcement” mechanical properties. The term an “effective reinforcement” is used to denote a MWCNT surrounded by a layer of the polymer matrix whose thickness is comparable to the MWCNT radius and whose conformation is changed as a result of its interactions with the MWCNT. The micro-mechanics procedure yielded the effective continuum mechanical properties for the MWCNT-reinforced poly-vinyl-ester-epoxy matrix composite mats with a random in-plane orientation of the MWCNTs as a function of the following composite microstructural parameters: the volume fraction of the MWCNTs, their aspect ratio, the extent of covalent functionalization of the MWCNT outer walls as well as a function of the mechanical properties of the matrix and the reinforcements.     

Design of automation for telerobots and the effect on performance,operator situation awareness,and subjective workload

In this article we review and assess human‐centered level of automation (LOA), an alternate approach to traditional, technology‐centered design of automation in dynamic‐control systems. The objective of human‐controlled LOA is to improve human‐machine performance by taking into account both operator and technological capabilities. Automation literature has shown that traditional automation can lead to problems in operator situation awareness (SA) due to the out‐of‐the (control) loop performance problem, which may lead to a negative impact on overall systems performance. Herein we address a standing paucity of research into LOA to deal with these problems. Various schemes of generic control system function allocations were developed to establish a LOA taxonomy. The functions allocated to a human operator, a computer, or both, included monitoring system variables, generating process plans, selecting an “optimal” plan and implementing the plan. Five different function allocation schemes, or LOAs, were empirically investigated as to their usefulness for enhancing telerobot system performance and operator SA, as well as reducing workload. Human participants participated in experimental trials involving a high fidelity, interactive simulation of a telerobot performing nuclear materials handling at the various LOAs. Automation failures were attributed to various simulated system deficiencies necessitating operator detection and correction to return to functioning at an automated mode. Operator performance at each LOA, and during the failure periods, was evaluated. Operator SA was measured using the Situation Awareness Global Assessment Technique, and perceived workload was measured using the NASA‐Task Load Index. Results demonstrated improvements in human‐machine system performance at higher LOAs (levels involving greater computer control of system functions) along with lower operator subjective workload. However, under the same conditions, operator SA was reduced for certain types of system problems and reaction time to, and performance during, automation failures was substantially lower. Performance during automation failure was best when participants had been functioning at lower, intermediate LOAs (levels involving greater human control of system functions). © 2000 John Wiley & Sons, Inc.     

Multi-scale ballistic material modeling of cross-plied compliant composites

The open-literature material properties for fiber and polymeric matrix, unit-cell microstructural characteristics, atomic-level simulations and unit-cell based finite-element analyses are all used to construct a new continuum-type ballistic material model for 0°/90° cross-plied highly-oriented polyethylene fiber-based armor-grade composite laminates. The material model is formulated in such a way that it can be readily implemented into commercial finite-element programs like ANSYS/Autodyn [ANSYS/Autodyn version 11.0, User Documentation, Century Dynamics Inc. a subsidiary of ANSYS Inc. (2007)] and ABAQUS/Explicit [ABAQUS version 6.7, User Documentation, Dessault Systems, 2007] as a User Material Subroutine. Model validation included a series of transient non-linear dynamics simulations of the transverse impact of armor-grade composite laminates with two types of projectiles, which are next compared with their experimental counterparts. This comparison revealed that a reasonably good agreement is obtained between the experimental and the computational analyses with respect to: (a) the composite laminates’ capability, at different areal densities, to defeat the bullets with different impact velocities; (b) post-mortem spatial distribution of damage within the laminates; (c) the temporal evolution of composite armor laminate back-face bulging and delamination; and (d) the existence of three distinct penetration stages (i.e. an initial filament shearing/cutting dominated stage, an intermediate stage characterized by pronounced filament/matrix de-bonding/decohesion and the final stage associated with the extensive back-face delamination and bulging of the armor panel).     

Iron nucleation mechanisms on vitreous carbon during electrodeposition from sulfate and chloride solutions

Iron nucleation mechanisms from aqueous solutions onto vitreous carbon electrode were comparatively investigated in iron sulfate and iron chloride systems by utilizing the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The investigated parameters were pH, scanning rate, iron concentration, deposition potential and temperature. It was found that iron nuclei population density decreased with increase of pH. On the other hand, the population density increased with increase of iron concentration and cathodic deposition potential. Increase of solution temperature resulted in the increase of nuclei population density in the sulfate system, while the dependence of nuclei population density on temperature in the chloride system was more complex. The experimental electrochemical data fitted the theoretical model describing progressive nucleation mechanisms, which was also confirmed by the AFM morphological studies. In addition, the atomic force microscopy was successful in determining the possible crystallographic orientations of electrodeposited iron nuclei.